.TH vangenu 1 "Version VERSION"
.ds -- \-\^\-
.ds b[ \fR[\|\fP
.ds b] \fR\|]\fP

.SH NAME
vangenu \- determine van Genuchten parameters from a pF curve

.SH SYNOPSIS
.B getstr
.B \*(b[\*(--help\*(b]
.B \*(b[\*(--Header\*(b]
.B \*(b[\*(--copyright\*(b]
.B \*(b[\*(--license\*(b]
.BI \*(b[\*(--alpha\   alpha\*(b]
.BI \*(b[--n\   n\*(b]
.BI \*(--thetar\   "residual_theta"
.BI \*(--thetas\   "theta_at_saturation"
.I filename

.SH DESCRIPION
.B vangenu
can determine the van Genuchten parameters alpha and n from pairs
of pF theta values. It uses Marquardt's non-linear regression to
do so.

Input is read from either 
.I filename
or standard input. If 
.I filename
is specified as a single dash
.RB `` \- '',
it is taken from standard input. Output is written to the standard
output. 

The input file must contain two columns, containing pF in the
first column and the corresponding theta value in the second.
The following shows an example:
.PP
.RS
.nf
.ft CW
0.4 0.370
1.0 0.360
1.4 0.34
1.7 0.30
2.0 0.28
2.4 0.24
2.7 0.23
.ft R
.fi
.RE

.SH OPTIONS
Options may be given as either standard
one-letter options, or GNU style long options. Long options start with
two dashes
.RB `` \*(-- ''
and may be truncated to any unambiguous abbreviation.

.TP
.B \*(--copyright
Show copyright information and exit

.TP
.B \*(--Header
Omit headers from output.

.TP
.B \*(--license
Print license information and exit.

.TP
.B \*(--help
Print help text and exit.

.TP
.BI \*(--alpha\   valua_for_alpha
Give the initial value for alpha. Note that unrealistic values can
cause the fitting process to crash.

.TP
.BI \*(--n\   value_for_n
Give the initial value for n. Note that unrealistic values can
cause the fitting process to crash.


.SH USAGE
All options cane be entered as GNU style long options or abbriviated
to the first letter op the option.

.SH EXAMPLES

vangenu ---alpha 0.04 -n 1.3 -thetas 0.46 -thetar 0.04 mydata.dat

.SH SEE ALSO
.BR vamps (1),
.BR vamps (5).


.SH AUTHOR
J. Schellekens
.br
schj@geo.vu.nl
.br
schj@xs4all.nl


.SH BUGS
The fitting process can crash if initial values deviate to much
from the optimal ones.
